One-pot synthesis of hyperbranched polymers via visible light regulated switchable catalysis

Switchable catalysis promises exceptional efficiency in synthesizing polymers with ever-increasing structural complexity. However, current achievements in such attempts are limited to constructing linear block copolymers. Here we report a visible light regulated switchable catalytic system capable of synthesizing hyperbranched polymers in a one-pot/two-stage procedure with commercial glycidyl acrylate (GA) as a heterofunctional monomer. Using (salen)CoIIICl (1) as the catalyst, the ring-opening reaction under a carbon monoxide atmosphere occurs with high regioselectivity (>99% at the methylene position), providing an alkoxycarbonyl cobalt acrylate intermediate (2a) during the first stage. Upon exposure to light, the reaction enters the second stage, wherein 2a serves as a polymerizable initiator for organometallic-mediated radical self-condensing vinyl polymerization (OMR-SCVP). Given the organocobalt chain-end functionality of the resulting hyperbranched poly(glycidyl acrylate) (hb-PGA), a further chain extension process gives access to a core-shell copolymer with brush-on-hyperbranched arm architecture. Notably, the post-modification with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) affords a metal-free hb-PGA that simultaneously improves the toughness and glass transition temperature of epoxy thermosets, while maintaining their storage modulus.

of 40 × 10 × 3 mm 3 were measured using the three-point bending mode at a temperature range from 25 to 200 °C.

Pendulum impact testing:
The test of impact strength was conducted through the plastic pendulum impact testing machine PTM7000 (Shenzhen SUNS Technology Stock Co., LTD., China).
(Salen)Co III Cl. Recrystallized (salen)Co II (6.0 g, 9.9 mmol) and p-toluenesulfonic acid monohydrate Methylene chloride (200 mL) was added to a 500 mL separatory funnel. Tosylate catalyst (5.0 g) was added to the funnel and agitated until the solid completely dissolved. The organic layer was rinsed with saturated aqueous NaCl (3 x 200 mL). The organic layer was dried over Na2SO4 and concentrated under reduced pressure. The solid was suspended in pentane and filtered to afford very dark green powder with 85% yield. In an argon filled glove box, (salen)Co III Cl complex (63.9 mg, 0.1 mmol), GA (23 μL, 0.2 mmol), and THF (1 mL) were charged into a 10 mL ampoule, which was wrapped in aluminum foil and equipped with a magnetic stir bar. The ampoule was then taken out of the glove box and allowed to be stirred under 1 atm CO at room temperature for 8 h. Dark green powder was obtained after GA and THF were evaporated under vacuum with 98% yield.

OMR-SCVP of GA with 2a as the inimer
See the Methods section of the main manuscript for detailed experimental procedures.

Visible light regulated switchable catalysis from ring-opening to OMR-SCVP with GA as a heterofunctional monomer.
See the Methods section of the main manuscript for detailed experimental procedures.

Chain extension of hb-PGA-Co III (salen) with MA
In an argon filled glove box, hb-PGA-Co III (salen) (0.96 g, Mn, SEC = 9.6 kDa, 0.1 mmol), MA (2.70 mL, 30 mmol), and THF (2 mL) were charged into a 25 mL ampoule, which was wrapped in aluminum foil and equipped with a magnetic stir bar. The ampoule was then taken out of the glove box and allowed to stirred at 25 o C under irradiation of a household white LED lamp with light intensity of 10 mW·cm -2 . A small aliquot of the polymerization mixture was taken out for 1 H NMR spectroscopy and the remained crude mixture was precipitated in cold methanol.

Preparation of hb-PGA-TEMPO/DGEBF
A certain amount of hb-PGA-TEMPO and DGEBF were dissolved in methylene chloride. Then most of solvent was rapidly removed using a rotary evaporator. The obtained mixture was further dried in a vacuum at 40 °C for 6 h. After which, 6 wt% EMI-2, 4 relative to epoxy resin was incorporated into the mixture and degassed for several minutes. Finally, the uncured mixture was decanted into a PTFE mold and underwent a programmed curing of 60 °C for 2 h, 150 °C for 8 h. For comparison, neat DGEBF were fabricated using the same process.

Synthesis of alkoxycarbonyl cobalt complex 3 2
A mixture of (salen)Co II (3 g, 4.95 mmol) and excess potassium persulfate was added to CH2Cl2. After degassed with CO (balloon) for 10 s, the reaction mixture was then treated with the respective alcohol (2.33 g, 24.75 mmol) and stirred for the indicated time in the dark, at room temperature, under 1 atm of CO. Reactions were tracked by TLC (3% MeOH in CH2Cl2). Upon completion, the product was precipitated by addition of heptane, filtered through Celite and washed several times with heptane to obtain a dark green powder, yield 91%.

Procedure for the synthesis of linear PGA
In an argon filled glove box, complex 3 (72.4 mg, 0.1 mmol), GA (0.34 mL, 3 mmol), and THF (1.16 mL) were charged into a 10 mL ampoule equipped with a magnetic stir bar. The ampoule was then taken out of the glove box and allowed to be stirred at 25 o C under irradiation of a household white LED lamp with light intensity of 10 mW·cm -2 . A small aliquot of the polymerization mixture was taken out for 1 H NMR spectroscopy and the remained crude mixture was precipitated in cold methanol.  (Table 1, entry 3).